bpo-34864: warn if "Prefer tabs when opening documents" set to "Always" (#10464)

* bpo-34864: warn if "Prefer tabs when opening documents" set to "Always"

* add NEWS entry

* address code review comments

* address second code review comments

* Add entry for idlelib/NEWS.txt.

1 files changed, 21 insertions, 4 deletions

diff --git a/Lib/idlelib/pyshell.py b/Lib/idlelib/pyshell.py
index 47eef43..81a97ef 100755
--- a/Lib/idlelib/pyshell.py
+++ b/Lib/idlelib/pyshell.py
@@ -38,6 +38,7 @@ from platform import python_version
 import re
 import socket
 import subprocess
+from textwrap import TextWrapper
 import threading
 import time
 import tokenize
@@ -1273,6 +1274,14 @@ class PyShell(OutputWindow):
         self.set_line_and_column()
         self.io.reset_undo()
 
+    def show_warning(self, msg):
+        width = self.interp.tkconsole.width
+        wrapper = TextWrapper(width=width, tabsize=8, expand_tabs=True)
+        wrapped_msg = '\n'.join(wrapper.wrap(msg))
+        if not wrapped_msg.endswith('\n'):
+            wrapped_msg += '\n'
+        self.per.bottom.insert("iomark linestart", wrapped_msg, "stderr")
+
     def resetoutput(self):
         source = self.text.get("iomark", "end-1c")
         if self.history:
@@ -1541,12 +1550,20 @@ def main():
             shell.interp.execfile(script)
     elif shell:
         # If there is a shell window and no cmd or script in progress,
-        # check for problematic OS X Tk versions and print a warning
-        # message in the IDLE shell window; this is less intrusive
-        # than always opening a separate window.
+        # check for problematic issues and print warning message(s) in
+        # the IDLE shell window; this is less intrusive than always
+        # opening a separate window.
+
+        # Warn if using a problematic OS X Tk version.
         tkversionwarning = macosx.tkVersionWarning(root)
         if tkversionwarning:
-            shell.interp.runcommand("print('%s')" % tkversionwarning)
+            shell.show_warning(tkversionwarning)
+
+        # Warn if the "Prefer tabs when opening documents" system
+        # preference is set to "Always".
+        prefer_tabs_preference_warning = macosx.preferTabsPreferenceWarning()
+        if prefer_tabs_preference_warning:
+            shell.show_warning(prefer_tabs_preference_warning)
 
     while flist.inversedict:  # keep IDLE running while files are open.
         root.mainloop()